Vladimir Falko

Partial ordering of dilute adsorbents on graphene

Location: Dahlem Center Seminar RoomTime: Monday 25.01.2010, 16h c.t.

We investigate a possibility of formation of a correlated state in a
dilute ensemble of adatoms randomly deposited on graphene. For the
adsorbents that reside in the middle of hexagons of the honecomb graphene
lattice, as well as for those that take position over the centre of the AB
bond, we find a tendency towards a spatially correlated state with a
hidden Kekule mosaic order. This effect emerges from the interaction
between the adatoms mediated by the Friedel oscillations of the electron
density in graphene. The problem is mapped onto the three-value random
Potts model, and the critical temperature of the partial ordering
transition is established using the cluster Monte-Carlo simulations. The
onset of the ordered state, as the system is cooled below the critical
temperature, is accompanied by an effective Brillouin zone folding and
opening of a gap in the electronic spectrum. For the adsorbents which
reside over carbon sites the corresponding partial ordering (similar to
the ordering transition in a random Ising model with ferromagnetic
coupling)
would result in the A-B sublattice symmetry breaking, also leading to the
spectral gap formation.